Power generation systems often include a power converter that is configured to convert an input power into a suitable power for application to a load, such as a generator, motor, electrical grid, or other suitable load. For instance, a power generation system, such as a wind turbine system, may include a power converter for converting variable frequency alternating current power generated at the generator into alternating current power at a grid frequency (e.g. 50 Hz or 60 Hz) for application to a utility grid. An exemplary power generation system may generate AC power using a wind-driven doubly fed induction generator (DFIG). A power converter can regulate the flow of electrical power between the DFIG and the grid.
Under certain conditions (e.g., transient power conditions), a high power mismatch between the rotor and the grid connection temporally exists and voltage transients become amplified such that a DC link voltage level can increase above normal allowed or rated levels. Various approaches have been utilized in the past to absorb or deflect power from the DC link during such excessive power level conditions. For example, fast acting shorting means, such as crowbar circuits, have been utilized to limit power flow into the DC link when grid faults or other transient events occur. More recently, dynamic brake systems have been utilized that include a resistor coupled to the DC link via a switch to dissipate power from the DC link. However, while such crowbar circuits and dynamic brakes are useful for preventing overvoltage conditions within the DC link, the power absorbed or deflected from the DC link is lost, thereby reducing the overall efficiency of the power generation system.
Accordingly, a system and method for operating a power generation system that allows power to be both deflected from the DC link during the occurrence of transient events and stored for subsequent discharge back to the DC link would welcomed in the technology. In addition, it would be desirable for the system to be further configured to operate as a dynamic brake when the option for power storage is unavailable to allow power to be dissipated from the DC link during transient events.